I made my opinion on the first few posts following the OP, and I will add something here. I've noted many posts here and on other sites referring to poor IT QA or legitimately stumbling on to this error and why it should be honored.
While there is no doubt it is shoddy programming, it doesn't make it OK to then purposely take advantage of it. A fare mistake that was loaded incorrectly and allowed to ticket, I can see that being UA's responsibility. In this case, it didn't ticket at the error rate and people are trying to manipulate the price.
I think an appropriate analogy in this case isn't a mispriced item at the store (price sticker of $1.50 instead of $150), but a customer purposely removing the correct $150, and putting a $1.50 price sticker on, going to the checkout in hopes the cashier doesn't notice.
Again, there is a difference between taking advantage of the store's error (UA mispricing their flights last month) vs. proactively trying to change the price when the correct price has been displayed.